ChitChat (was WhatsMac) is a native Mac wrapper around WhatsApp's web client, WhatsApp Web. It allows you to receive Notification Center notifications for new messages, and adds some useful keyboard shortcuts:

• Start a new conversation: ⌘N
• Search past conversations: ⌘F
• Jump to your 1st..9th most recent conversation: ⌘1..⌘9

Inspired by, and in small part based on, Messenger for Mac, created by Rasmus Andersson. WhatsMac uses some code from this project.